The present invention relates to a device and a method for measuring an electric current and, in particular, to a device and a method for measuring the electric current flowing through one or a plurality of conductors of an array of several electric conductors which are arranged in close proximity to one another.
For potential-free current measurement it. is known to place two magnetic-field-sensitive sensors on both sides of an electric conductor. Such an arrangement is schematically shown in FIG. 1, where two magnetic-field-sensitive sensors 2 and 4 are arranged on both sides of an electric conductor 6. By means of the magnetic-field-sensitive sensors 2 and 4, the magnetic field generated by a current flowing through the conductor 6 is measured. The current in the conductor is determined by forming the difference between the output signals of the two magnetic-field-sensitive sensors 2 and 4; this principle permits an existing, gradient-free magnetic field to be eliminated when the current is being measured. The above-described arrangement is disadvantageous insofar as 2n sensors are required, when the currents in n conductors are to be measured simultaneously. The known method is also problematic when the currents through a plurality of conductors are to be measured and when the conductors are arranged in closely spaced relationship with one another. This will give rise to a magnetic field gradient at the location of a conductor due to the current of a neighbouring conductor so that the current measurement will be disturbed. The influence of the magnetic field gradient caused by the current in the neighbouring conductor cannot be compensated for.
It is the object of the present invention to provide a device and a method for measuring the current through one or a plurality of conductors of an array of n conductors making use of a reduced number of magnetic-field-sensitive sensors, which additionally permit an exact detection of the current through one of the conductors even if the individual conductors of the conductor array are arranged in close proximity to one another.
This object is achieved by a current measuring device according to claim 1 and a method according to claim 8.
The present invention provides a current measuring device for measuring the current through one or a plurality of conductors of an array of n conductors, n being a natural numberxe2x89xa72, in the case of which n+1 magnetic-field-sensitive sensors are arranged in such a way that two respective magnetic-field-sensitive sensors are arranged adjacent a respective conductor. Furthermore, a unit for reading out output signals of the magnetic-field-sensitive sensors is provided. Finally, the current measuring device is provided with a unit for calculating the current through one or a plurality of conductors on the basis of the read output signals and on the basis of coefficients which describe the influence of currents flowing through each of the n conductors and of a constant magnetic field on the output signal of each of the magnetic-field-sensitive sensors.
The present invention thus permits a reduction of the required magnetic-field-sensitive sensors from 2n to n+1, when the current flowing through n conductors is to be detected. In addition, the present invention permits a compensation of influences, which are caused by closely spaced, current-carrying conductors, on the current measurement in one conductor. It follows that the present invention provides, on the one hand, a relatively simple current measuring device, which provides, on the other hand, exact results in the case of electric conductors arranged in close proximity to one another.
The magnetic-field-sensitive sensors are preferably Hall sensors which are monolithically produced on a semiconductor substrate together with the evaluation electronics, i.e. the read-out unit and the calculating unit, and, preferably, together with a memory for storing the coefficients.
The present invention additionally provides a method of measuring the current through one or a plurality of conductors of an array of n conductors, n being a natural numberxe2x89xa72, wherein the output signals of n+1 magnetic-field-sensitive sensors are first read out, two respective ones of these sensors being arranged adjacent a respective conductor. Subsequently, the current through one or a plurality of the conductors is calculated on the basis of the read output signals and on the basis of coefficients which describe the influence of currents flowing through each of the n conductors and of a constant magnetic field on the output signal of each of the magnetic-field-sensitive sensors.
Preferred embodiments of the method according to the present invention additionally comprise the step of executing a calibration measurement so as to calculate the coefficients. In so doing, the coefficients are determined as matrix coefficients in such a way that a defined current is conducted through each of the conductors in turn while the other conductors do not carry a current. In addition, a further calibration measurement is carried out in the case of which a constant magnetic field, i.e. a gradient-free magnetic field having a known magnitude, is applied to the magnetic-field-sensitive sensors, while no current flows through the conductors. For calculating the current flowing through one or a plurality of the conductors, the sensor signals of all the magnetic-field-sensitive sensors are then linearly interconnected via a matrix operation making use of the coefficient matrix determined.
As has been mentioned hereinbefore, the magnetic-field-sensitive sensors are preferably Hall sensors. These Hall sensors are sensitive to perpendicularly impinging magnetic fields so that the sensors are arranged between the conductors or, displaced upwards or downwards, in the space between the conductors.
In addition, the present invention also permits the use of sensors which are sensitive to magnetic fields impinging parallel to the surface, e.g. field plates. These sensors are arranged in such a relation to the conductors that the magnetic field generated by the conductors impinges on the sensors substantially parallel to the surface thereof.